Department of Neurosciences, ExpORL, and Parenting and Special Education Research Unit, University of Leuven, 3000 Leuven, Belgium.
J Neurosci. 2014 Jan 22;34(4):1523-9. doi: 10.1523/JNEUROSCI.3209-13.2014.
The temporal envelope of speech is an important cue contributing to speech intelligibility. Theories about the neural foundations of speech perception postulate that the left and right auditory cortices are functionally specialized in analyzing speech envelope information at different time scales: the right hemisphere is thought to be specialized in processing syllable rate modulations, whereas a bilateral or left hemispheric specialization is assumed for phoneme rate modulations. Recently, it has been found that this functional hemispheric asymmetry is different in individuals with language-related disorders such as dyslexia. Most studies were, however, performed in adults and school-aged children, and only a little is known about how neural auditory processing at these specific rates manifests and develops in very young children before reading acquisition. Yet, studying hemispheric specialization for processing syllable and phoneme rate modulations in preliterate children may reveal early neural markers for dyslexia. In the present study, human cortical evoked potentials to syllable and phoneme rate modulations were measured in 5-year-old children at high and low hereditary risk for dyslexia. The results demonstrate a right hemispheric preference for processing syllable rate modulations and a symmetric pattern for phoneme rate modulations, regardless of hereditary risk for dyslexia. These results suggest that, while hemispheric specialization for processing syllable rate modulations seems to be mature in prereading children, hemispheric specialization for phoneme rate modulation processing may still be developing. These findings could have important implications for the development of phonological and reading skills.
言语的时间包络是影响言语可懂度的重要线索。有关言语感知的神经基础理论假设，左右听觉皮层在分析不同时间尺度的言语包络信息方面具有功能特异性：右半球被认为专门处理音节率调制，而音位率调制则假定为双侧或左半球特异性。最近，人们发现这种功能半球不对称性在与语言相关的障碍（如阅读障碍）个体中存在差异。然而，大多数研究都是在成年人和学龄儿童中进行的，对于在阅读习得之前，非常年幼的儿童在这些特定速率下的神经听觉处理如何表现和发展，人们知之甚少。然而，研究未识字儿童处理音节和音位率调制的半球专门化可能会揭示阅读障碍的早期神经标志物。在本研究中，在具有高和低阅读障碍遗传风险的 5 岁儿童中测量了音节和音位率调制的人类皮质诱发电位。结果表明，无论阅读障碍的遗传风险如何，右半球都偏向于处理音节率调制，而对于音位率调制则呈现对称模式。这些结果表明，虽然处理音节率调制的半球专门化在阅读前儿童中似乎已经成熟，但处理音位率调制的半球专门化可能仍在发展中。这些发现对于语音和阅读技能的发展可能具有重要意义。
